Improving the UV resistance of blister heat seal packaging color cards requires a multi-dimensional approach involving material selection, additive application, structural optimization, and process control to address the degradation, fading, and mechanical property decline caused by UV radiation.
The UV resistance of the material matrix is fundamental to performance improvement. blister heat seal packaging color cards typically use thermoplastics such as polyvinyl chloride (PVC), polyester (PET), or polypropylene (PP). PET, due to its aromatic rings and ester groups in its molecular chain structure, has a high UV absorption threshold, which can delay photo-oxidation reactions. While PVC is low-cost, its chlorine-containing structure is susceptible to UV attack, requiring modification to enhance stability. For example, introducing acrylate units through copolymerization can reduce the polarity of the PVC molecular chain, decrease UV-induced free radical generation, and thus improve weather resistance.
The synergistic addition of UV absorbers and stabilizers is a key technological approach. UV absorbers (such as benzotriazoles and benzophenones) can convert UV energy into heat energy through intramolecular hydrogen bond transfer or isomerization reactions, preventing the material's molecular chains from breaking. Light stabilizers (such as hindered amines, HALS) can capture free radicals and interrupt the photo-oxidation chain reaction. In practical applications, the additive ratio needs to be adjusted according to the material type. For example, PVC-based color cards require the simultaneous addition of UV absorbers and metal soap heat stabilizers to synergistically inhibit dehydrochlorination and photodegradation; while PET-based color cards, due to their high heat resistance, can preferentially use benzotriazole absorbers to reduce the impact of additives on transparency.
Optimizing the interface between the color layer and the substrate can reduce UV penetration. The color layer of blister heat seal packaging color cards is usually attached to the substrate surface through printing or co-extrusion processes. If there are gaps at the interface between the color layer and the substrate, UV rays can easily penetrate the color layer and directly act on the substrate, accelerating aging. Co-extrusion processes, by simultaneously melting and extruding the masterbatch and the substrate resin to form a molecularly bonded composite structure, can significantly improve interfacial adhesion. For example, using double-layer co-extrusion technology to composite a color layer containing UV absorbers with a high-impact PET substrate can reduce the color difference rate of the color card under UV irradiation.
Surface coating technology can construct a physical protective barrier. Coating the surface of color cards with a transparent coating containing nano-titanium dioxide or zinc oxide reduces UV penetration through reflection and scattering. The small size and high specific surface area of nanoparticles allow for more uniform dispersion within the coating, forming a continuous UV-blocking layer. Furthermore, fluoropolymer coatings (such as polytetrafluoroethylene) reduce UV-induced surface oxidation reactions due to their low surface energy, while simultaneously improving the color cards' abrasion and chemical resistance.
Precise control of the heat-sealing process prevents performance degradation caused by localized overheating. Excessive temperature or time during heat sealing can lead to degradation of the substrate at the color card edges, creating weak areas and accelerating UV aging. Optimizing the heat-sealing mold design (e.g., using a gradual temperature zone) and adjusting process parameters (e.g., controlling the heat-sealing temperature at 90%–95% of the substrate's melting temperature) ensures uniform fusion of the heat-sealed layer and avoids localized overheating. Simultaneously, selecting heat-sealing adhesives with good substrate compatibility (such as polyurethane) reduces stress concentration during heat sealing, improving the overall weather resistance of the color cards.
Environmental adaptability testing guides performance optimization. By simulating accelerated UV aging tests under different climatic conditions (such as high temperature and high humidity, and low temperature and freezing), the performance degradation pattern of color cards in complex environments can be evaluated. For example, in a humid and hot environment, the synergistic effect of UV light and moisture accelerates material hydrolysis, causing the edges of the color cards to peel up; while in a dry and high-temperature environment, the thermal oxidation reaction induced by UV light is more significant. Based on the test results, additive formulations or process parameters can be adjusted accordingly, such as increasing the amount of moisture-curing light stabilizers, to improve the stability of the color cards in humid and hot environments.
